Councils and schools are being forced to raid existing budgets to ensure that a Government scheme to offer free school lunches to infants goes ahead, according to a survey.

Under plans first announced by Deputy Prime Minister and Lib Dem leader Nick Clegg last year, all five to seven-year-olds will be entitled to the meals from this September.

But a new poll by the Local Government Association (LGA), suggests that just weeks before the initiative is due to be introduced, some local authorities are facing a shortfall in the funding they need to ensure it can be delivered.

Government funding worth £150 million in total was handed to councils to cover the cost of bringing school kitchens and dining facilities up to scratch. Funding will be provided separately to pay for the dinners.

The LGA's survey of 75 councils found that nearly half (47%) said they had not received enough money from the Department for Education (DfE) to cover the full cost of the work they needed to do to ensure that schools in their area were ready to provide universal free meals for infants.

The shortfall across those councils that responded totals around £25.9 million, the association estimated.

Of those that said that they did not have enough money, 49% said that the council would help to make up the difference, with just over a third (37%) saying at least some of the cash would come from school funds.

Authorities had also reported that money could be taken from general school funding intended for school repairs and maintenance, the association said.

The LGA said it had calculated that councils without enough money for the scheme have had to find an estimated £488,000 on average to ensure that pupils will get the meals they will be entitled to.

It added that some schools will give pupils packed lunches and others will use portable kitchens to ensure they can offer the free lunches when the new school year starts, and work will continue on options for providing hot meals.

Councillor David Simmonds, chairman of the LGA's children and young people board, said: "When the youngest pupils go back to school next month, their mums and dads will expect them to receive a free and nutritious meal. Some councils already provided this service, and now that it has become government policy we are determined to ensure every child is provided for.

"There's no doubt that dishing up a nutritious lunch for every young pupil will improve the experience of school and help them concentrate in lessons.

"Councils and schools have been working really hard to make this happen within this ambitious timescale. But it cannot be right that for some councils, money set aside for maintenance has instead had to be spent plugging the shortfall in money which government should have provided for meals.

"This research makes it clear central government has not provided schools with enough money to do the essential work necessary to give 1.5 million children a free meal at lunchtime. It is councils and schools who are picking up the bill for this work, at a time when budgets are already squeezed and tough decisions are being taken."

Shadow education secretary Tristram Hunt said: "Hard-pressed schools and councils are being forced to bail out David Cameron's Government because of its own incompetence.

"Nick Clegg announced the policy without doing the maths first. It's more evidence that voters cannot trust a word the Liberal Democrats say."